Battle for the Belt: Season 3, Episode 21 – Risks & Management During the Seed Fill Stage of Soybean

Season 3, Episode 21 of Battle for the Belt is now available: https://www.youtube.com/watch?v=qpALweA-Ow8

Across Ohio, soybean plants are moving into critical reproductive stages as we reach mid-August. In the Battle for the Belt study, planting dates ranged from March 27 through June 24, with the earliest plantings at the R5 (beginning seed) or R6 (full seed) stages. A soybean plant reaches R5 when a seed measuring at least 1/8 inch is present in a pod at one of the four uppermost nodes with a fully developed leaf. This is a highly sensitive period, as the plant has already shifted to seed fill and cannot easily compensate for lost leaf area or reduced photosynthesis. Therefore, stressors such as disease, insects, or hail can have significant impacts on yield potential.

Scouting is strongly recommended at this time to monitor insect feeding, disease pressure, or other plant damage. Although leaf loss is especially damaging during seed fill, fungicide applications are not generally recommended this late in the season. In some areas of Ohio, drought has also added stress, limiting soil moisture and restricting nutrient availability for seed development, which in turn may reduce final seed size. Visible nutrient deficiencies may also appear now, since nitrogen, phosphorus, and potassium absorbed earlier in vegetative growth are redistributed to support seed filling.

While in-season management options are limited once soybeans reach seed fill, long-term strategies can help reduce the risk of stress in future seasons. Practices such as no-till, cover cropping, and manure application improve soil organic matter and water-holding capacity, providing resilience under dry conditions. Fertility management is also most effective when addressed before planting, ensuring the crop has adequate nutrient availability throughout its growth cycle. For additional resources, the Science for Success team—funded by the United Soybean Board—offers research-based fact sheets at https://soybeanscienceforsuccess.org. For more information on this topic, please see “The Soybean Growth Cycle: Important Risks, Management and Misconceptions” at: https://resources.ipmcenters.org/resource.cfm?rid=45261&vid=33931

What is happening in the field?

Late last week parts of the state received rain, and our Western and Northwest locations had about 4/10^th and 3/10^th of an inch, respectively. The first planting date of corn reached R5 or the dent stage. In this stage a dent forms on the kernel and you can follow the milk line which shows the border between liquid and startch in the kernel. Dry matter accumulation at this stage is important and this usually marks about 30 days or 337 to 360 GDDs (Nielson, 2021) to maturity. Furthermore, at Western, gray leaf spot is still the most prominent disease in corn and can be found in most of the planting dates that are in reproductive stages.

At the Wooster location, the first four planting dates of corn have been in the reproductive stages. However, northern corn leaf blight (NCLB) has been found in the fifth planting date (6/23) for a few weeks.  NCLB is the most prominent disease at this location and can be found in all five planting dates. Though this is the most detrimental for planting date four (6/2) and five.

The Northwest location has suffered from dry weather (Figure 2) and is on the U.S. drought monitor as an abnormally dry area. Because of the dry weather there has been limited disease pressure. However, in the first two planting dates (3/27, 4/16) zipper ears have been prominent, showing there was heat or drought stress during pollination (Figure 3). Pollination occurred for these planting dates at the end of June and beginning of July, the hottest part of the season.

For soybean, all planting dates are in the reproductive stages, and there is limited disease pressure at all locations. The first planting dates at all locations are in the mid R5 stage, which is discussed earlier in this article.

Table 1. Precipitation, soil temperature, average air temperature, cumulative growing degree days (GDDs), and stage at the Western Agricultural Research Station, the Northwest Agricultural Research Station, and Wooster Campus. Weather data retrieved from: https://weather.cfaes.osu.edu/.

For additional information, you can follow our research highlights through the C.O.R.N. articles and YouTube updates during this growing season. The full Battle for the Belt video series is also available on the Ohio State Agronomy YouTube channel.